Updating aging LiDAR for flood mitigation modeling

Extensive flooding throughout low-lying areas of the City of Storm Lake, Iowa has resulted in millions of dollars in property damage in recent years. To identify the root causes of this flooding, EOR performed a comprehensive survey and assessment of the City’s stormwater infrastructure and constructed a watershed model using PCSWMM that encompassed 700 hectares of mixed urban and agricultural land and 18 km of storm sewers. The state-wide LiDAR dataset was severely out of date due to construction of a large detention basin and the reconstruction of a roadway. We collected survey-grade GPS and updated the LiDAR in a process contained entirely within a file geodatabase using Terrains in ArcGIS 10.3. Best practices will be discussed, including the use of 3D line features - the importance of which points toward the continued benefit to using traditional land surveying techniques to supplement small-scale LiDAR acquisition. Updating LiDAR with natural or anthropogenic alterations to the terrain is especially poignant in light of the move toward 2D flood modeling that our ever-increasing computing power has facilitated, and is essential for accurate and complete representations of drainage pathways and storage volumes, among other potential concerns. Flooding was determined to be caused by a combination of factors including insufficient inlet capacity, insufficient pipe capacity, and tailwater effects due to the flat drainage ditch at the stormsewer outfall. Due to this variety of factors and the high cost of replacing or reconstructing sizeable sections of infrastructure, solutions were identified in strategic upstream areas that could retain and detain runoff before it entered the storm sewer system, thus freeing up capacity and significantly reducing the frequency and severity of flooding events. Project costs for engineering and construction total $2 million USD. The project has been awarded, with construction starting March 2018 and completed by April 2019.